A Telecom Serving System (TSS) is one of the functions of a telecom network (wireline, wireless, internet, data, VoIP, etc) that allows devices to travel within the coverage area of the network and receive services. The function of a telecom serving system is to acquire the geographic location of the end user devices, and deliver calls, text messages, and other services to the devices at the appropriate location in the network. The location of the device is generally maintained in a subscriber server or database that stores a profile for the subscriber. For example, in a 2G or 3G cellular network, the subscriber profile may be stored in a Home Location Register (HLR) or a Visitor Location Register (VLR). In a 4G network, such as an IP Multimedia Subsystem (IMS) or a Long Term Evolution (LTE) network, the subscriber profile may be stored in a Home Subscriber Server (HSS).
In order to monitor the location of a device, telecom service standards in many networks require the device to inform the network whenever it moves from one location area to the next (also referred to as a location update procedure). When the device determines that it has moved to a new location area, the device sends a location update request to the network. The network then updates the subscriber profile for the subscriber based on the location update request. The location update procedure may also require that the device periodically report its location at a set time interval to the network. If the location of the device has changed, then the network updates the subscriber profile for the subscriber.
If the network subsequently receives a call or a text message (e.g., SMS) for the subscriber, the serving element in the network (e.g., MSC) is able to query the subscriber database (e.g., HLR or VLR) to determine the present location of the end user device. With the introduction of 3G and 4G networks, dual mode or multiple mode devices may be used to access different types of technology networks. For example, a device may be able to register with a 2G circuit-switched network, such as a CDMA network, while also being able to register with a 4G packet-switched network, such as an LTE network. In such an instance, the subscriber may roam from one technology network to another (e.g., from the 2G CDMA network to the 4G LTE network) while expecting seamless services. Presently, an HSS in an LTE network may not support subscriber registration in the CDMA network, while an HLR in the CDMA network may not support subscriber registration in the LTE network. Unfortunately, the different technology networks may not be able to communicate effectively to provide seamless services.